SDDM is a modern display manager for X11 and Wayland aiming to be
fast, simple and beautiful. It uses modern technologies like QtQuick,
which in turn gives the designer the ability to create smooth,
animated user interfaces.

You will need to edit /etc/rc.d/rc.4 to get this work.
Put the section that refers to sddm before the others:

# Look for SDDM as well:
if [ -x /usr/bin/sddm ]; then
  exec /usr/bin/sddm
fi
